Typical examples of tensioning ratchets are described in European Patent EP 0 455 085 B1, U.S. Pat. 5,282,296 or German Patent 296 07 275 U1. In the case of these tensioning ratchets the direction reversal bars have an identical, in each case circular cross-sectional shape.
The curvature radius of the outer circumferential face of the direction reversal bars coming into contact with the tensioning means and their invariable axial distance to one another are selected in such a way that they define a winding-on shaft with a circular cross section to the extent of the distance existing between the direction reversal bars. The distance of the direction reversal bars is sufficiently great in order to be able to insert an end section of the particular tensioning means there.
As a result of the direction reversal bars being jointly turned about the axis of rotation of the winding-on shaft formed thereby, the end section of the tensioning means inserted between them is pulled along and a multi-layer coil, whose layers lying tightly together due to the tensile forces applied on the tensioning means are held on the winding-on shaft with high surface friction and correspondingly high self-locking, is formed on the winding-on shaft.
To mount the winding-on shaft and at the same time to be able to couple it securely and under uniform loading with the shoulder, in the case of tensioning ratchets of the known type, the console is normally formed in a U-shape with a base from whose ends one side emerges respectively. A circular bearing opening, whose opening radius with slight over dimension is adapted to the curvature radius of the circumferential faces of the direction reversal bars, is formed in the vicinity of the free ends of the sides. The ends of the direction reversal bars of the winding-on shaft lie in the bearing openings with play, so that they can be turned about an axis of rotation running through the midpoint of the bearing openings.
For tautening the tensioning means the known ratchets are equipped with a tensioning lever, which is connected torsionally-fixed to the direction reversal bars and can be pivoted about the axis of rotation of the winding-on shaft. The tensioning lever, moreover, normally comprises at least one ratchet gear wheel, which is mounted concentrically to the axis of rotation of the winding-on shaft and is connected torsionally-fixed to the tensioning lever. The ratchet gear wheel cooperates with a pawl, the so-called “locking slide”, mounted on the console, which when the ratchet gear wheel is turned, accompanying the pivoting of the tensioning lever, engages in the gaps existing between the teeth of the ratchet gear wheel and locks the turning position of the winding-on shaft reached in each case.
Since in the tautened condition both the tensioning means coiled up on the tensioning ratchet and the console coupled on the respective shoulder are tightened, the console in the ideal case is held in a line of force running through the shoulder, the axis of rotation of the winding-on shaft and the tensioning means.
For safe retention of the cargo to be secured high tension is normally necessary in the tensioning means. In order to be able to adjust this by means of the tensioning ratchet, the known tensioning ratchets are usually equipped with tensioning levers of considerable length. The ratio of the lever arm length to the radius of the coiled up webbing results in the gearing of the applied force. This force is limited on the one hand by the ability of the user, who through his bodily strength or weight brings the tensioning lever to the required tensioning position. On the other hand, the maximum permitted manual force to be applied by a user is constrained by European Standard EN12195-2.
Attempts have been made through longer tensioning levers or through higher gearing of the leverage forces to further increase the tensioning forces which can be applied by means of a tensioning ratchet, while adhering to the limits mentioned above. In practice, however, it has been shown that the tensioning forces produced in this way lead to such strains on the overall construction that individual parts of the tensioning ratchet are overstressed. A design meeting the requirements regarding constant maximum stress and operating reliability of a tensioning ratchet permitting further increased tensioning forces would entail a no longer manageable weight and dimensions equally hard to handle.